linux-kernel - Re: fbcon: remove soft scrollback code (missing Doc. patch)

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Message-ID: <alpine.LFD.2.21.2009302216230.333514@eddie.linux-mips.org>
Date:   Wed, 30 Sep 2020 22:29:36 +0100 (BST)
From:   "Maciej W. Rozycki" <macro@...ux-mips.org>
To:     Adam Borowski <kilobyte@...band.pl>
cc:     Pavel Machek <pavel@....cz>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Daniel Vetter <daniel@...ll.ch>,
        Yuan Ming <yuanmingbuaa@...il.com>, Willy Tarreau <w@....eu>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        NopNop Nop <nopitydays@...il.com>,
        张云海 <zhangyunhai@...ocus.com>,
        Andy Lutomirski <luto@...capital.net>
Subject: Re: fbcon: remove soft scrollback code (missing Doc. patch)

On Fri, 18 Sep 2020, Adam Borowski wrote:

> > > Note that scrollback hasn't actually gone away entirely - the original
> > > scrollback supported by _hardware_ still exists.
> > > 
> > > Of course, that's really just the old-fashioned text VGA console, but
> > > that one actually scrolls not by moving any bytes around, but by
> > > moving the screen start address. And the scrollback similarly isn't
> > > about any software buffering, but about the ability of moving back
> > > that screen start address.
> 
> > Could we pause this madness? Scrollback is still useful. I needed it
> > today... it was too small, so command results I was looking for
> > already scrolled away, but... life will be really painful with 0 scrollback.
> > 
> > You'll need it, too... as soon as you get oops and will want to see
> > errors just prior to that oops.
> 
> I concur -- this a serious usability regression for regular users.  Linus:
> you have a serial cable on your main dev machine, so do I, but hardly any
> regular people do -- that's restricted to mostly IPMI and such.
> 
> And without some kind of scrollback, there's no way of knowing why eg.
> your rootfs failed to mount (there was some oops, but its reason was at
> the beginning...).  Or, any other problem the user would be able to solve,
> or pass the error messages to someone more knowledgeable.
> 
> I also wonder why did you choose to remove softscrollback which is actually
> useful, yet leave hardscrollback which doesn't come to use on any
> non-ancient hardware:
> * on !x86 there's no vgacon at all
> * on x86, in-tree drivers for GPUs by Intel, nVidia and AMD (others are
>   dead) default to switching away from vgacon
> * EFI wants its own earlycon
> ... thus, the only niche left is nVidia proprietary drivers which, the last
> time I looked, still used CGA text mode.

 For the record I keep using the console scrollback all the time, and FWIW 
I have gone through all the hoops required to keep using VGA hardware 
emulation and its console text mode with my most recent laptop, which is a 
ThinkPad P51; no longer manufactured, but still hardly an obsolete device 
by today's standards I believe.  Sadly this video adapter setup has its 
shortcomings which used not to be there with my older hardware, which I 
find a functional regression to be blamed on the manufacturer, but I have 
learnt to live with that as I found no alternative I would find 
comfortable to work with.

 So no, it's not that nobody uses that stuff anymore, and not with 
obsolete hardware either.

  Maciej